[libunwind][WebAssembly] Make libunwind compilable (#92192)

This tries to make Wasm compilable in LLVM tree with CMake for
non-Emscripten platform.

This
- Adds `-D__USING_WASM_EXCEPTIONS__` when you compile with
`-fwasm-exceptions` (like other EH options) in Clang
- Exclude `UnwindLevel1.c`, `UnwindRegistersSave.S`, and
`UnwindRegistersRestore.S` when compiling with Wasm
- Changed some `__USING_WASM_EXCEPTIONS__` to `__wasm__`; they should be
applied when compiling with Wasm w/o exceptions.
- Define some unused macros to make it compile

Fixes #72771.

libunwind/include/__libunwind_config.h

@@ -180,6 +180,10 @@
 #endif
 #define _LIBUNWIND_HIGHEST_DWARF_REGISTER                                      \
   _LIBUNWIND_HIGHEST_DWARF_REGISTER_LOONGARCH
+#elif defined(__wasm__)
+// Unused
+#define _LIBUNWIND_CONTEXT_SIZE 0
+#define _LIBUNWIND_CURSOR_SIZE 0
 # else
 #  error "Unsupported architecture."
 # endif

libunwind/src/UnwindLevel1.c

@@ -31,7 +31,8 @@
 #include "libunwind_ext.h"
 #include "unwind.h"
 
-#if !defined(_LIBUNWIND_ARM_EHABI) && !defined(__USING_SJLJ_EXCEPTIONS__)
+#if !defined(_LIBUNWIND_ARM_EHABI) && !defined(__USING_SJLJ_EXCEPTIONS__) &&   \
+    !defined(__wasm__)
 
 #ifndef _LIBUNWIND_SUPPORT_SEH_UNWIND
 

libunwind/src/UnwindRegistersRestore.S

@@ -20,7 +20,7 @@
   .text
 #endif
 
-#if !defined(__USING_SJLJ_EXCEPTIONS__)
+#if !defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__wasm__)
 
 #if defined(__i386__)
 DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_x86_jumpto)
@@ -1232,7 +1232,7 @@ DEFINE_LIBUNWIND_FUNCTION(_ZN9libunwind19Registers_loongarch6jumptoEv)
 
 #endif
 
-#endif /* !defined(__USING_SJLJ_EXCEPTIONS__) */
+#endif /* !defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__wasm__) */
 
 NO_EXEC_STACK_DIRECTIVE
 

libunwind/src/UnwindRegistersSave.S

@@ -20,7 +20,7 @@
     .text
 #endif
 
-#if !defined(__USING_SJLJ_EXCEPTIONS__)
+#if !defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__wasm__)
 
 #if defined(__i386__)
 
@@ -1177,6 +1177,6 @@ DEFINE_LIBUNWIND_FUNCTION(__unw_getcontext)
 
   WEAK_ALIAS(__unw_getcontext, unw_getcontext)
 
-#endif /* !defined(__USING_SJLJ_EXCEPTIONS__) */
+#endif /* !defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__wasm__) */
 
 NO_EXEC_STACK_DIRECTIVE

libunwind/src/libunwind.cpp

@@ -26,7 +26,7 @@
 #include <sanitizer/asan_interface.h>
 #endif
 
-#if !defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__USING_WASM_EXCEPTIONS__)
+#if !defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__wasm__)
 #include "AddressSpace.hpp"
 #include "UnwindCursor.hpp"
 
@@ -348,7 +348,7 @@ void __unw_remove_dynamic_eh_frame_section(unw_word_t eh_frame_start) {
 
 #endif // defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
 #endif // !defined(__USING_SJLJ_EXCEPTIONS__) &&
-       // !defined(__USING_WASM_EXCEPTIONS__)
+       // !defined(__wasm__)
 
 #ifdef __APPLE__